The present invention relates to a vehicular hydraulic braking system with a hydraulic brake booster, in general, and more particularly to a system including antiskid equipment.
There are already known hydraulic braking systems in which the pressure of the brake fluid from an auxiliary pressure source is supplied to the wheel brake actuating cylinders by means of a control valve operated in dependence on a brake pedal travel and loaded by a travel simulator when the auxiliary pressure source is intact and in which the brake fluid pressure is furnished by a master cylinder, in particular by a tandem master cylinder, which is also operated in dependence on the brake pedal travel, in the event of failure of the auxiliary pressure source.
In one known vehicular braking system of this type which is known from the German published patent application DE-OS No. 24 43 545, a control valve is provided having an outer and an inner slide which are movable relative to each other. The inner slide is connected with the brake pedal. One side of the outer slide is acted upon by the outlet pressure of the control valve, while the other side of the outer slide is acted upon by a stack of Belleville spring washers serving as a travel simulator. As long as the auxiliary pressure source, which may include a pressure accumulator or a compressing pump, is operational, the pressure prevailing at the outlet of the control valve is supplied to the wheel brake operating cylinders via the working chambers of a tandem master cylinder and via antiskid control valves. The brake fluid enters the working chambers from reservoir chambers by flowing past deflectable seals of the respective master cylinder pistons opposite to their closing direction. If there is a failure of the auxiliary pressure source, the tandem master cylinder will be able to operate in the usual manner as the master cylinder pistons will be entrained for joint movement with the brake pedal after a short idle travel, so that their seals will move beyond respective feed ports. A disadvantage in this arrangement is that it is impossible to recognize defects at the seals as long as the auxiliary pressure source generates pressure. This, of course, may have grave consequences once the auxiliary pressure source fails.